The present invention relates to a process for the preparation of polymer fibers in which a polymer solution is cooled and subjected to shearing forces during the course of polymer precipitation.
The polymeric fibers thus obtained can be employed as a feedstock for the preparation of other useful products such as paper-like products, synthetic leather, textile products such as fibrous nonwovens, and also as a filler material in fiber-reinforced plastics.
It is well-known according to prior procedures that polyolefin fibers can be prepared during the polymerization stage by subjecting the reaction mass to a sufficiently strong shear stress; such a procedure is described, inter alia, in Belgian Pat. No. 533,382, examples 8 and 9; U.S. Pat. No. 3,231,515, example 3; and French Pat. No. 1,137,457. With this process a fibrous gel is produced in the reactor as described in Kunststoff-Rundschau, January 1968, page 38. Since the polymerization and the fiber formation take place in the same reaction vessel, the process conditions cannot be conveniently adjusted so that an optimum course of the two processes is ensured. The known method, moreover, has the drawback that a voluminous viscous mass is produced in the reactor, which has an unfavorable effect on the reactor capacity and causes difficulties when the polymerizate is being discharged from the reactor. Further, if stirrers are used, the fibers formed in the reactor will wrap around them, so that the polymerization has to be interrupted frequently for removing these entangled fibers.
In British Pat. Specification No. 1,142,253, the suggestion has been made to allow the fiber formation to take place outside the reactor and, according to this operation, a polymer solution is cooled and vigorously stirred, with the consequence that the shearing forces cause the polymer to precipitate from the solution in fibrous form. This process also has the same drawback that the fiber preparation has to be frequently interrupted for removing the fiber deposits from the stirrer.
The present invention provides a process permitting continuous preparation of the polymer fibers without involving the drawbacks mentioned above.